Taking 3 mm thick 6082-T6 aluminum alloy as the base material for laser-MIG composite welding, this paper investigates the influence of laser power and wire feed speed on the weld forming, microstructure and mechanical properties, and the porosity defect of welded joints under different power was analyzed. Results show that the weld seam forming was the the best with the laser power of 1 900 W, wire feed speed of 4 m/min, and the microhardness of the joint from the base material to the center of the weld shows a trend of first decreasing and then increasing. Moreover, the heat affected zone exists the phenomenon of softening, and tensile strength and elongation reach up to 313 MPa and 6.18%, respectively. The center of the weld is organized as fine equiaxed grains, and the fusion zone is composed of columnar crystal growing perpendicular to the fusion line. In addition, the number, size and porosity of the joint pores increased with the increasing of laser power.

In this paper, the longitudinal butt-welding experiment of 1 mm thickness 304 stainless steel pipe was carried out by laser self-fusion welding technology. Based on the control variable experiment of two factors and four levels, microstructure characteristics were tested by optical microscope, X-ray diffractometer and scanning electron microscope. Taking the surface forming and microhardness as the index, the optimum welding parameters were adopted with a laser power of 3.5 kW, welding speed of 30 mm/s, and the focal position of + 2 mm. Results show that the weld center is composed of fine equiaxed austenite and dendritic ferrite, and there are fine columnar dendrites at the edge of the weld, which grow along the direction perpendicular to the fusion line whose dimension is proportional to the welding heat input. Under the optimal welding parameters, the microhardness of heat affected zone is 221 HV, and the microhardness of weld center is 214 HV. There is a negative correlation between microhardness and heat input in the corresponding regions of different welded joints.

In order to achieve fast and high precision calibration of rotating structured light in the plane, a self-calibration method of rotating structured light was proposed based on the curved welding seam in space. Firstly, a camera was calibrated to obtain its internal and external parameters, weld track was pre-extracted through image processing, and the rotation axis of the steering gear was calibrated with a two-dimensional target. Secondly, the structured light was fixed to the initial pose by the steering gear head, and the plane calibration of the structured light was carried out by using the principle of constant cross ratio. The scanning welding parts of the structured light was controlled by the gantry of the rotating steering gear, and the structured light was controlled to be always perpendicular to the tangent line of the track at the scanning point. Moreover, the required rotation angle from the initial posture to the vertical posture was obtained. The self-calibration of the structured light plane at the scanning point was completed through the formula of plane rotation around any axis. Experimental results show that the plane equation of structured light is obtained by cross ratio invariant principle and plane rotation self-calibration of structured light at the scanning points, respectively. The root mean square of coefficient difference is 1.35×10-3, which has high precision and simple operation.

Laser-weaving welding process of SUS316 stainless steel was studied in this paper. The test was carried out by changing scanning amplitude, frequency, welding speed, laser power, defocusing amount, etc. The welding forming and mechanical property were tested and compared at different scanning mode. Results show that rectangular weld with good appearance can be achieved when the vertical amplitude is ≥ 0.15 mm. Lower frequency results in dentate weld, and higher frequency will lead to undercut more easily. Good appearance can be achieved with suitable frequency from 300 Hz to 400 Hz. To avoid dentate weld, the ratio of frequency to weld speed should be more than 10. Laser power and defocusing amount mainly affect weld depth and width. Compared with normal laser welding, the weld of laser-weaving welding is stronger. When the weld width is about 1 mm，stainless steel with 1 mm thickness can be processed as overlap joint with tensile strength 698 MPa, which is 1.34 times higher than base metal.

In order to investigate the influence of laser power, scanning speed and powder feeding rate on the properties of Fe-based alloy powder cladding on the surface of 45 steel, single-pass forming test of laser cladding was carried out using orthogonal test scheme. The ratio of width to height, dilution rate and hardness of the cladding layer were used as the evaluation indexes to judge the performance and quality of the cladding layer, The influence of each cladding process parameter was judged by range analysis, and the best combination of single cladding process parameters was obtained based on multi-objective optimization method of genetic algorithm. Results show that the powder feeding rate is the main factor affecting the hardness of cladding layer, and the laser power is the second one. Scanning speed is the main factor affecting the height and width of cladding layer. The feeding rate is the main factor affecting the dilution rate. The optimal combination of process parameters is obtained, i.e., laser power 2 056 W, scanning speed 8.75 mm/s, and powder feeding rate 2.198 g/min, which provides guidance for the selection of process parameters of laser cladding iron-based powder for 45 steel.

Cobalt-based laser cladding layer was prepared on the surface of 45 steel, and the microstructure of the cladding layer, the morphology of the molten pool and the wear resistance of the cladding layer were characterized by metallographic microscope (OM), scanning electron microscope (SEM), X-ray energy spectrometer (EDS) and friction and wear testing machine. Results show that the quality of the cladding layer increases first and then decreases with the increase of the laser power. When the laser power reaches 2 000 W, the quality of the cladding layer is the best, the molten pool is relatively stable, and there are no defects such as pores. The microstructure of the cladding layer changes from coarse and dispersed columnar crystals to fine and uniform equiaxed crystals, and finally to coarse columnar crystals. In the friction and wear test, with the increase of laser power, the wear mechanism of the cladding layer changes from massive exfoliation to particle wear. The wear resistance of the cladding layer is the best, and the real-time friction coefficient is the most stable. The wear rate is only 1.3×10-4 mm3/(N·m) under laser power of 2 000 W.

In this paper, the temperature field distribution of high entropy alloy (HEA) CoCrFeMnNi fabricated by selective laser melting (SLM) is numerically simulated by Ansys finite element analysis software. Considering the thermophysical parameters varying with temperature, the finite element model of selective laser melting is developed. The loading of Gaussian cone heat source is realized by inserting parametric design language into Ansys-Workbench. The influence of power and speed on the temperature field in the forming process was studied. The simulation results show that with the increase of SLM laser power and the decrease of SLM scanning speed in single-layer and multi-channel simulation, the weld pool length and width of HEA CoCrFeMnNi fabricated by SLM are increasing.

With the acceleration of industrial modernization, three-dimensional laser point cloud technology has begun to appear in industrial target detection, and the segmentation and extraction of laser point clouds have become the key to industrial detection. Commonly used 3D point cloud segmentation methods, such as region growing segmentation, RANSAC (random sampling consistent) segmentation, K-means (K-means clustering), cannot achieve high-level target segmentation and extraction. In this paper, MEMS (Micro Electromechanical System) 3D cameras are used to collect point cloud data of 4 groups of targets, and the mesh RANSAC segmentation algorithm is used to encapsulate the 3D point cloud of the target, which is rasterized into mesh modules. In order to obtain the final target extraction result and successfully complete the counting statistics, the point cloud in each mesh module is processed with plane rough segmentation, module integration, and fine segmentation on the segmented target using European clustering. Experimental results show that the segmentation completeness of the mesh RANSAC segmentation algorithm proposed in this paper is 91.0%, and the average time is 8.25 s, which is better than the other three traditional algorithms. It also successfully completes the count.

In order to solve the problems of low efficiency of traditional manual method and low adaptability of single-line laser measurement in tire tread depth measurement, a set of tire tread depth measurement method based on multi-line laser is proposed in this paper. This method obtains the images of tire with a multi-line laser stripe by measuring device. Three-dimensional point data of the center point of the laser stripe on the tire surface is obtained by the triangulation technique, and the tire groove points and tire tread points are screened out from the 3D point cloud data. The tire groove points are synthesized into a curved surface, the distances between the tire pastry and the groove surface are successively calculated, and the depth of each groove is obtained to determine the wear condition of the tire. The difference between the measured results and the depth gauge is less than 0.1 mm, which can meet the requirements of tire tread depth measurement.

This paper presents a new algorithm for center extraction of line structured laser light. This algorithm is based on the maximally stable extremal regions (MSER) algorithm to extract the stripe effective regions quickly and efficiently, which takes advantage of the feature that the stripe region has high contrast with the background region. Based on the idea of scanning only the effective area of the light strip, the traditional algorithm is easy to be affected by noise and low detection efficiency in the scanning process of image redundancy information. In addition, the gray center of gravity method was used to extract the center of effective light stripe regions detected by MSER in view of the deviation error of the center of light stripe caused by the different number of laser stripe cross sections involved in the calculation. Experimental results show that the proposed algorithm can quickly extract the center of the strip, which is nearly 19 times faster than the Steger algorithm, and this proposed algorithm has high anti-noise performance.

In order to further improve the accuracy rate of large-scale and various kinds of 3D point clouds, this paper proposes a Convolutional Neural Network (CNN) that builds a relationship of K-nearest neighbor graphs in a local area. The key is to learn the relation between points. After the sample group finished sampling, the point cloud model is constructed and the point cloud is classified through learning the profound relationship between points and characteristics of the central point. Because this method integrated from the partial to the whole features, it makes this method to be sensitive to the shape and robust. The final experiment demonstrates that the precision rate of this method reached 92.5% on the public data set ModelNet40. Compared with the existing 3D point cloud classification algorithms, this algorithm could integrate local features and global features more effectively. Therefore, it will further increase the accuracy of 3D point cloud model classification.

In order to analyze the effect of laser surface modification treatment of magnesium alloy materials for sports equipment, magnesium alloy materials were preprocessed, and the laser melting treatment process was determined. Moreover, the hardness, wear resistance and corrosion resistance of the surface of magnesium alloy materials were calculated, and the database of the detection data in research period was developed, which was analyzed by using SPSS17.0 software. Results show that when the laser power used in the laser melting modification treatment is 3 kW, the hardness, wear resistance and corrosion resistance of the modified magnesium alloy surface are improved most obviously. Experiments show that laser melting treatment can enhance the hard content of the surface of magnesium alloy materials, strengthen precipitation, refine α-Mg grains, reduce the spacing between β phases, and form a denser Al2O3 oxide film. These results make the distribution of impurity elements in the magnesium alloys more uniform, thereby improving the physical, chemical and mechanical properties of the surface of the magnesium alloy material, and improving the hardness, corrosion resistance and wear resistance of the magnesium alloy material.

In order to prevent the lens from being broken or burnt during long-term high-power laser cleaning and ensure the service life and stability of the optical head, this paper uses the Solidworks software for structural design and three-dimensional modeling of the collimation system, galvanometer system and focusing lens group in the laser cleaning head, and the feasibility study of the structural parameters of each system of the optical head is carried out. The temperature field simulation is carried out by using ANSYS Workbench, and the reliability of the model design is verified through temperature detection and laser cleaning experiments. Results show that the energy density of the incident light spot of each lens is lower than the corresponding damage threshold, and the temperature variation of each component of the laser head obtained by simulation is within the reliable range. The designed bald head model is reliable, which can meet the working requirements. This paper provides the corresponding theory and method for the independent research and development of high-power laser cleaning heads.

Diode lasers are often used as the light source of LiDAR for their high energy conversion efficiency, small size and good reliability. A novel collimator based on integrated aspheric cylindrical lens are proposed, which have different surface types in two surfaces, and it could collimate the diode laser in both directions. According to Fermat′s principle and beam expanding collimation theory, the surface parameters were determined preliminarily. The optical system of the light source projection was completed, which was optimized with the minimum spot radius and maximum luminous flux as the goals and the MEMS scanning mirror size as the limiting factor. Results show that the divergence angle in the meridional direction is 2 mrad, and the divergence angle in the sagittal direction is 9.6 mrad. The collimation effect is close to the average angular resolution of MEMS-LiDAR in the market, the lens volume is 10×10×24 mm3, the total length of the transmitter system is 40 mm, and the luminous rate of the system is 98.6%. It meets the requirements of MEMS-LiDAR for the collimation of the light source, the integration degree and stability of the transmitter system.

The phase shift phenomenon occurs in the propagation process of surface acoustic waves excited by laser under Thermoelastic effect. The phase variation law of surface wave and the interaction mechanism between surface wave and defect in aluminum cylinder are numerically simulated by finite element method. Numerical results show that the negative phase of the surface wave generated by laser is the strongest, the negative phase moves to the positive phase in the propagation process, and the phase difference gradually decreases. The intensity of the positive and negative phases is roughly equal at about 180°. After that, the positive phase continues to strengthen and the negative phase continues to weaken, and its phase reverses once every time it travels around the circle. The surface reflection wave produced by the defect has the same phase change phenomenon. Through scanning diagram B, it is found that RRcw becomes fuzzy with the increase of defect Angle, and RRccw becomes obvious with the increase of defect Angle. It shows that the length of reflection wave generation time is proportional to the degree of interference. Based on this, a reasonable detection range is proposed for the surface defects of cylindrical materials. The numerical simulation of defects with different depths indicated that the change of depth made the P-wave peak delay in receiving time. The propagation path of P-wave peak was speculated and the corresponding formula was proposed to prove it. The calculated results were in good agreement with the simulated results, and the defect depth information could be quantified by this formula. The above research results provide an effective reference for ultrasonic detection of surface defects of columnar materials.

Compared with the common imaging, the polarization imaging contains more reflection and scattering information of the object surface. In this paper, polarization imaging method is used to obtain the degree of polarization image of skin surface under different light sources to study the effects of laser and LED light sources in the same waveband and laser and LED light sources in different wavebands on polarization imaging, in order to find a suitable type and waveband of polarization imaging lighting source for special disease. Results show that the information entropy and average gradient of laser polarization image are higher than those of LED polarization image under the same waveband light source. For the local imaging of erythema and mole on the skin, the image detail performance under green waveband illumination is better than that under red waveband illumination, providing more information for laser polarization imaging to improve the accuracy of skin state diagnosis.

To investigate the efficacy of laser point irradiation combined with salvia miltiorrhiza ligustrazine intraarticular administration in the treatment of knee osteoarthritis(KOA), 96 KOA patients were randomly divided into control group (n=48, salvia miltiorrhiza ligustrazine injection) and observation group (n=48, laser point irradiation combined with salvia miltiorrhiza ligustrazine intraarticular administration). The clinical efficacy, knee pain, knee function, knee range of motion and plasma levels of INTERleukin-1 β (IL-1β), C-reactive protein (CRP), cartilage oligomer matrix protein (COMP) and matrix metalloproteinase-3 (MMP-3) were compared between the two groups before and after treatment. Results showed as follows: the total effective rate of observation group (93.75%) was higher than that of control group (77.08%) (P<0.05). Compared with before treatment, VAS score, IL-1β, CRP, COMP and MMP-3 levels in 2 groups decreased after treatment (P<0.05), Lysholm score and knee motion increased (P<0.05), but the improvement of above indexes in observation group was better than that in control group (P<0.05). It is concluded that laser acupoint irradiation combined with salvia miltiorrhiza ligustrazine intra-articular intra-articular administration has satisfactory effect on knee osteoarthritis.

A total of 6 564 academic papers and 110 highly cited papers on optical imaging in biomedical field from 1990 to 2020 in Web of Science database were selected as the research objects, and the distribution characteristics, co-authors and keywords co-occurrences were analyzed by using the statistics and bibliometric software CiteSpace. Results show that photoacoustic imaging, nanoparticles, optical biopsy, Oct, deep tissue imaging, cell imaging, probes, cancer theranostics, drug delivery, carbon nanotubes and other aspects are the research hotspots in this field. Near infrared-Ⅱ spectral fluorescence imaging, semiconductor polymer nanoparticles, photoacoustic imaging, optical biopsy, tumor theranostics have become the frontier topics in biomedical optical imaging. The research in the following aspects are particularly prominent: deep tissue optical imaging, organic semiconductor materials for phototherapy and biopsy, photoacoustic imaging contrast agents and two-dimensional titanium nanosheets for multimodal imaging-guided cancer theranostics.